This invention is generally directed to layered hydrogenated amorphous silicon alloy imaging members; and more specifically, the present invention is directed to layered photoconductive imaging members comprised of a number of layers of, for example, hydrogenated amorphous silicon, hydrogenated amorphous germanium, or alloys thereof, and certain charge transport layers. Therefore, in one embodiment of the present invention, there is provided a layered photoresponsive imaging member comprised of a supporting substrate; a charge transport layer comprised of various components inclusive of, plasma deposited hydrogenated amorphous silicon, silicon oxides, silicon nitrides, silicon carbides, boron nitrides, amorphous carbon, and organosilanes; and a photogenerating layer comprised of number of thin alternating p, n components, inclusive of hydrogenated n-type amorphous silicon alloys doped with phosphorus and hydrogenated p-type amorphous silicon alloys, doped with boron. Further, in an alternative specific embodiment of the present invention there is provided a layered photoresponsive imaging member wherein the alternating p, n thin layers are comprised of infrared sensitive materials such as hydrogenated amorphous germanium. Moreover, the imaging members of the present invention can be comprised of a supporting substrate, a charge transport layer of hydrogenated amorphous silicon, and a phtotgenerating layer comprised of a number of thin alternating p, n components, inclusive of hydrogenated n-type amorphous silicon alloys, or hydrogenated p-type amorphous silicon alloys. These imaging members can be incorporated into electrophotographic, and in particular, xerographic imaging and printing systems wherein, for example, the latent electrostatic patterns which are formed can be developed into images of high quality and excellent resolution. Additionally, the members of the present invention possess high charge acceptance values in excess of 1,000 volts for example; excellent low dark decay characteristics; superior charging ability without an increase in dark decay; and further, these members can be of a very desirable thickness from, for example, about 10 microns or less. Furthermore, the photoresponsive imaging members of the present invention when incorporated into xerographic imaging and printing systems are insensitive to humidity and corona ions generated permitting the formation of acceptable images of high resolution for an extended number of imaging cycles.
Electrostatographic imaging, particularly xerographic imaging processes, are well known, and are extensively described in the prior art. In these processes, a photoresponsive or photoconductor material is selected for the formation of the latent electrostatic image thereon. The conductor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material; and in many instances, a thin barrier layer is situated therebetween to prevent charge injection from the substrate, which could adversely affect the quality of the resulting image. Examples of known useful photoconductive materials include amorphous selenium, alloys of selenium such as selenium-tellrium, selenium-arsenic, and the like. Additionally, there can be selected as the photoresponsive imaging member various organic photoconductive materials including, for example, complexes of trinitrofluorenone and polyvinylcarbazole. Recently there has been disclosed layered organic photoresponsive devices with aryl amine hole transporting molecules, and photogenerating layers, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Also known are amorphous silicon photoconductors, reference for example U.S. Pat. Nos. 4,265,991 and 4,225,222. There is disclosed in the '991 patent an electrophotographic photosenstive member comprised of a substrate, and a photoconductive overlayer of amorphous silicon containing 10 to 40 atomic percent of hydrogen and having a thickness of 5 to 80 microns. Additionally, this patent describes several processes for preparing amorphous silicon. In one process embodiment, there is prepared an electrophotographic photosensitive member by heating the member present in a chamber to a temperature of 50 degrees Centigrade to 350 degrees Centigrade, introducing a gas with silicon and hydrogen atoms, providing an electrical discharge in the chamber by electric energy to ionize the gas, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstronms per second by utilizing an electric discharge thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. Although the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 1,000 for example, unacceptable low quality images of poor resolution with many deletions may result. With further cycling, that is subsequent to 1,000 imaging cycles and after 10,000 imaging cycles, the image quality may continue to deteriorate often until images are partially deleted.
Further, there is disclosed in the prior art amorphous silicon photoreceptor imaging members containing, for example, stoichiometric silicon nitride overcoatings; however, these members in some instances generate prints of low resolution as a result of the band bending phenomena. Additionally, with the aforementioned silicon nitride overcoatings, the resolution loss can in many instances be extreme thereby preventing, for example, and image formation whatsoever.
There are also illustrated in copending applications photoconductive imaging members comprised of amorphous silicon. Accordingly, for example, there is illustrated in copending application U.S. Ser. No. 695,990, entitled Electrophotographic Devices Containing Compensated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, an imaging member comprised of a supporting substrate and an amorphous hydrogenated silicon composition containing from about 25 parts per million by weight to about 1 percent by weight of boron compensated with substantially equal amounts of phosphorus. Furthermore, described in copending application U.S. Ser. No. 548,117, entitled Electrophotographic Devices Containing Overcoated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of a supporting substrate, an amorphous silicon layer, a trapping layer comprised of doped amorphous silicon, and a top overcoating layer of stoichiometric silicon nitrides. More specifically, there is disclosed in this copending application an imaging member comprised of a supporting substrate, a carrier transport layer comprised of uncompensated or undoped amorphous silicon; or amorphous silicon slightly doped with p or n-type dopants such as boron or phosphorus, a thin trapping layer comprised of amorphous silicon which is heavily doped with p or n-type dopants such as boron or phosphorus; and a top overcoating layer of specific stoichiometric silicon nitride, silicon carbide, or amorphous carbon. However, one disadvantage with this imaging member is that the trapping layer introduces a dark decay component which reduces the charge acceptance for the imaging member.
Additionally, described in copending application U.S. Ser. No. 662,328, entitlled Heterogeneous Electrophotographic Imaging Members of Amorphous Silicon, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of hydrogenated amorphous silicon photogenerating compositions, and a charge transporting layer of plasma deposited silicon oxide containing at least 50 atomic percent of oxygen. The imaging member of the present invention is comprised of similar components as illustrated in the aforementioned application with the primary exceptions that there is selected for the imaging member of the present invention a photogenerating layer containing a number of thin alternating p, n components.
Other representative prior art disclosing amorphous silicon imaging members, including those with overcoatings, are U.S. Pat. Nos. 4,460,669; 4,465,750; 4,394,426; 4,394,425; 4,409,308; 4,414,319; 4,443,529; 4,452,874; 4,452,875; 4,483,911; 4,359,512; 4,403,026; 4,416,962; 4,423,133; 4,460,670; 4,461,820; 4,484,809; and 4,490,453. Additionally, patents that may be of background interest with respect to amorphous silicon photoreceptor members include, for example, U.S. Pat. Nos. 4,359,512; 4,377,628; 4,420,546; 4,471,042; 4,477,549; 4,486,521; and 4,490,454.
Further, additional representative prior art patents that disclose amorphous silicon imaging members include, for example, U.S. Pat. No. 4,357,179 directed to methods for preparing imaging members containing high density amorphous silicon or germenium; U.S. Pat. No. 4,237,501 which discloses a method for preparing hydrogenated amorphous silicon wherein ammonia is introduced into a reaction chamber U.S. Pat. Nos. 4,359,514; 4,404,076; 4,403,026 4,397,933; 4,423,133; 4,461,819, 4,237,151; 4,356,246; 4,361,638 4,365,013; 3,160,521; 3,160,522; 3,496,037; 4,394,426; and 3,892,650. Of specific interest are the amorphous silicon photoreceptors illustrated in U.S. Pat. Nos. 4,394,425; 4,394,426 and 4,409,308 wherein overcoatings such as silicon nitride and silicon carbide are selected. Examples of silicon nitride overcoatings include those with a nitrogen content of from about 43 to about 60 atomic percent.
Additionally, precesses for depositing large area defect free films of amorphous silicon by the glow discharge of silane gases are described in Chittick et al., the Journal of the Electrochemical Society, Volume 116, Page 77, (1969). Further, the fabrication and optimization of substrate temperatures during amorphous silicon fabrication is illustrated by Walter Spear, the Fifth International Conference on Amorphous and Liquid Semiconductors presented at Garmisch Partenkirchen, West Germany in 1973. Other silicon fabrication processes are described in the Journal of Noncrystalline Solids, Volumes 8 to 10, Page 727, (1972), and the Journal of Noncrystalline Solids, Volume 13, Page 55, (1973).
Although the above described amorphous silicon photoresponsive members, paraticularly those disclosed in the copending applications, are suitable in most instances for their intended purposes there continues to be a need for improved members comprised of amorphous silicon. Additionally, there is a need for amorphous silicon imaging members that posses desirable high charge acceptance values, low charge loss characteristics in the dark, and photosensitivity extending to the red and infrared regions of the spectrum. Furthermore, there continues to be a need for improved amorphous silicon imaging members with specific charge transport layers, and certain thin multilayers of photogenerating components. Also, there is a need for hydrogenated amorphous silicon imaging members with transport layers of plasma deposited silicon oxides, silicon nitrides, silicon carbides, boron nitrides, amorphous carbon, and organosilanes. Further, ther is a need for imaging members with the aforementioned charge transport layers, and alternating multilayers exceeding 10, for example, of hydrogenated or halogenated amorphous silicon; hydrogenated, or halogenated amorphous germanium; or alloys thereof with dopants therein. Furthermore, there is a need for amorphous silicon imaging members with low surface potential decay rated in the dark, and photosensitivity in the visible nad the near infrared wavelength range. There is also a need for amorphous silicon alloy imaging members with thin layers, less than 0.5 micron for example, of 10 to about 100, of a p-type hydrogenated amorphous silicon-germanium alloy, and n-type hydrogenated amorphous silicon-germanium alloy thereby enabling members with infrared sensitivity, and low dark decay characteristics. Moreover, there is a need for the aforementioned imaging members that possess low drak decay characteristics, acceptable charging abilities without increases in dark decay, and wherein images of superior resolution can be generated.